The goal of the proposed research plan is to investigate an unexplored and important function of p130Cas in cellular physiology, i.e., its role in regulating cell death and survival. p130Cas, originally identified as a major tyrosine-phosphorylated protein in v-Crk or v-Src transformed cells, is a multifunctional cell signal assembly protein. It contains multiple structure motifs and interact with a number of signaling molecules, such as Crk, Src, and FAK. Consistent with its structural characteristics, p130Cas has been found to be functionally involved in cell transformation, adhesion, migration and actin organization. It is essential for normal animal development. Mutant mice lacking p130Cas die in utero showing marked systemic congestion and growth retardation. Function of p130Cas in cell death/survival regulation, however, has not been studied. During the course of our study on regulation of protein tyrosine phosphorylation and cell growth, we found p130Cas to be a key player in tyrosine phosphatase LAR-induced apoptosis. LAR dephosphorylates and destabilizes the p130Cas protein. The down regulation of p130Cas by LAR leads to activation of a caspase pathway and induces apoptosis. Restoring p130Cas protein level alleviates the LAR-induced apoptosis. These data suggest a new function of p130Cas in regulating cell death/survival and a new mechanism by which the p130Cas protein is regulated. The present proposal is designed to investigate the function and mechanism of p130Cas in regulating cell death/survival. We will use a combination of biochemical, molecular, and cell biological techniques to identify specific signaling molecules and signal transduction pathways, through which p130Cas transduces cell death/survival signals. We will investigate the physiological relevance of p130Cas-mediated cell death by examining the regulation and function of p130Cas during anoikis, a form of cell death caused by detachment of epithelial and endothelial cells from their substratum, and in growth factor deprivation induced cell death, in both of which protein tyrosine phosphorylation/dephosphorylation play a critical role. Finally, the new mechanism regulating p130Cas protein level will also be investigated. The proposed study will increase our knowledge on function and mechanism of p130Cas, shed light on our general understanding of signal transduction, regulation of cell death/survival, and cell growth, and help designing therapeutic reagents to induce/prevent apoptosis in treating human diseases.